1. Field of the Invention
The present invention relates to an X-ray diagnostic apparatus generating a road map for a blood vessel structure.
2. Description of the Related Art
In intervention or angiographic examination, a catheter is inserted into a blood vessel from, for example, the joint of a leg and is guided to a target region through the blood vessel. This catheter or a guide wire inserted in the catheter is pushed forward to a target position under X-ray fluoroscopic observation. However, the blood vessel cannot be seen in an X-ray image unless enhanced by a contrast medium. Keeping injecting the contrast medium to visualize the blood vessel may result in renal failure. For this reason, a road map function is provided, which displays an image sensed after a contrast medium is injected once and an X-ray fluoroscopic image upon superimposing them. This function allows the operator to discriminate the position of a blood vessel to a certain extent without injecting any contrast medium, and hence is often used especially when a blood vessel structure is complicated and it is difficult to push a catheter or a guide wire into the blood vessel. According to this road map function, however, the occurrence of movement of the bed, rotation of the arm to change the observation direction, slight movement (stirring) of the patient, or the like makes it necessary to re-generate a road map image. Frequently re-generating a road map image leads to increases in examination time and the amount of contrast medium used.
In order to solve such problems, a 3D road map in which a road map image generated by using a 3D image and a fluoroscopic image are superimposed on each other is expected to be effective in reducing the amount of contrast medium used and shortening the examination time.
In order to mechanically superimpose a 3D image and an X-ray image, a method of generating a positional shift table may be used. However, since no specific limitation is imposed on angles to be used for medical treatment, a large amount of calibration data is required. This method cannot follow up the movement of a patient during medical treatment.
In academic conferences and the like, there has been proposed a method of performing calibration by extracting a catheter from a fluoroscopic image assuming that the catheter travels through a blood vessel. In a region with a complicated blood vessel structure, however, there is a risk of misinterpreting the correspondence between blood vessels. In addition, the shape of a blood vessel may be changed by the catheter. Furthermore, if a patient moves, it is very difficult to make correction by using the above method.